Підвищення ефективності сепарації пилу у вихрових апаратах із зустрічними закрученими потоками із циліндричною сепараційною камерою (ВАЗЗПЦ) для підприємств хімічних та будівельних матеріалів

Актуальною проблемою, яка постає сьогодні перед вітчизняною промисловістю, є вдосконалення техніки і технології охорони навколишнього середовища в цілому, і, зокрема, зменшення рівня запиленості атмосферного повітря.Вирішення проблеми міститься у процесі сепарації пилу у ВАЗЗПЦ і безперервним вивантаженням уловлюваного пилу стосовно хімічних та будівельних матеріалів

Mononuclear Rhodium(II) and Iridium(II) Complexes Supported by Tetradentate Pyridinophane Ligands

The tetradentate ligands <i>N</i>,<i>N</i>′-dialkyl-2,11-diaza­[3,3]­(2,6)­pyridinophane (^RN4, where R = Me or <i>t</i>Bu) were employed to synthesize and fully characterize [(^RN4)­M^I(COD)]⁺ complexes (M = Rh or Ir; COD = cyclooctadiene). Interestingly, these complexes exhibit accessible oxidation potentials and can generate detectable [(^RN4)­M^II(COD)]²⁺ complexes, which were characterized by electron paramagnetic resonance and high-resolution electrospray ionization mass spectrometry. Moreover, a rare mononuclear [(^MeN4)­Rh^II(COD)]²⁺ complex was isolated and crystallographically characterized, allowing for a direct comparison with its rhodium­(I) analogue. The detailed characterization of such paramagnetic rhodium­(II) and iridium­(II) complexes enables further investigation of their redox reactivity

The Aerobic Oxidation of a Pd(II) Dimethyl Complex Leads to Selective Ethane Elimination from a Pd(III) Intermediate

Oxidation of the Pd^II complex (N4)­Pd^IIMe₂ (N4 = <i>N</i>,<i>N</i>′-di-<i>tert</i>-butyl-2,11-diaza­[3.3]­(2,6)­pyridinophane) with O₂ or ROOH (R = H, <i>tert</i>-butyl, cumyl) produces the Pd^III species [(N4)­Pd^IIIMe₂]⁺, followed by selective formation of ethane and the monomethyl complex (N4)­Pd^IIMe­(OH). Cyclic voltammetry studies and use of 5,5-dimethyl-1-pyrroline-<i>N</i>-oxide (DMPO) as a spin trap suggest an inner-sphere mechanism for (N4)­Pd^IIMe₂ oxidation by O₂ to generate a Pd^III-superoxide intermediate. In addition, reaction of (N4)­Pd^IIMe₂ with cumene hydroperoxide involves a heterolytic O–O bond cleavage, implying a two-electron oxidation of the Pd^II precursor and formation of a transient Pd^IV intermediate. Mechanistic studies of the C–C bond formation steps and crossover experiments are consistent with a nonradical mechanism that involves methyl group transfer and transient formation of a Pd^IV species. Moreover, the (N4)­Pd^IIMe­(OH) complex formed upon ethane elimination reacts with weakly acidic C–H bonds of acetone and terminal alkynes, leading to formation of a new Pd^II–C bond. Overall, this study represents the first example of C–C bond formation upon aerobic oxidation of a Pd^II dimethyl complex, with implications in the development of Pd catalysts for aerobic oxidative coupling of C–H bonds

The Conformational Flexibility of the Tetradentate Ligand ^tBuN4 is Essential for the Stabilization of (^tBuN4)Pd^III Complexes

The conformationally flexible tetradentate pyridinophane ligand ^tBuN4 effectively lowers the oxidation potential of (^tBuN4)­Pd^II complexes and promotes their facile chemical and electrochemical oxidation, including unpredecented aerobic oxidation reactivity. While the low potential of a number of Pd^II (and Pt^II) complexes supported by various <i>fac</i>-chelating polydentate ligands is often attributed to the presence of a coordinating group in the axial position of the metal center, no detailed electrochemical studies have been reported for such systems. Described herein is the detailed electrochemical investigation of the effect of ligand conformation on the redox properties of the corresponding Pd^II complexes. These Pd complexes adopt different conformations in solution, as supported by studies using variable scan rate, variable-temperature cyclic voltammetry (CV), differential pulse voltammety, and digital CV simulations at variable scan rates. The effect of the axial amine protonation on the spectroscopic and electrochemical properties of the complexes was also investigated. A number of new Pd^III complexes were characterized by electron paramagnetic resonance, UV–vis spectroscopy, and X-ray diffraction including [(^tBuN4)­Pd^IIICl₂]­ClO₄, a dicationic [(^tBuN4)­Pd^IIIMe­(MeCN)]­(OTf)₂, and an unstable tricationic [(^tBuN4)­Pd^III­(EtCN)₂]³⁺ species. Although the electron-rich neutral complexes (^tBuN4)­PdMeCl and (^tBuN4)­PdMe₂ are present in solution as a single isomer with the axial amines not interacting with the metal center, their low oxidation potentials are due to the presence of a minor conformer in which the ^tBuN4 ligand adopts a tridentade (κ³) conformation. In addition, the redox properties of the (^tBuN4)Pd complexes show a significant temperature dependence, as the low-temperature behavior is mainly due to the contribution from the major, most stable conformer, while the room-temperature redox properties are due to the formation of the minor, more easily oxidized conformer(s) with the ^tBuN4 ligand acting as a tridentate (κ³) or tetradentate (κ⁴) ligand. Overall, the coordination to the metal center of each axial amine donor of the ^tBuN4 ligand leads to a lowering of the Pd^II/III oxidation potential by ∼0.6 V. These detailed electrochemical studies can thus provide important insights into the design of new ligands that can promote Pd-catalyzed oxidation reactions employing mild oxidants such as O₂

Oxidative C–C Bond Formation Reactivity of Organometallic Ni(II), Ni(III), and Ni(IV) Complexes

The use of the tridentate ligand 1,4,7-trimethyl-1,4,7-triazacyclononane (Me₃tacn) and the cyclic alkyl/aryl C-donor ligand -CH₂CMe₂-<i>o</i>-C₆H₄- (cycloneophyl) allows for the synthesis of isolable organometallic Ni^II, Ni^III, and Ni^IV complexes. Surprisingly, the five-coordinate Ni^III complex is stable both in solution and the solid state, and exhibits limited C-C bond formation reactivity. Oxidation by one electron of this Ni^III species generates a six-coordinate Ni^IV complex, with an acetonitrile molecule bound to Ni. Interestingly, illumination of the Ni^IV complex with blue LEDs results in rapid formation of the cyclic C-C product at room temperature. This reactivity has important implications for the recently developed dual Ni/photoredox catalytic systems proposed to involve high-valent organometallic Ni intermediates. Additional reactivity studies show the corresponding Ni^II species undergoes oxidative addition with alkyl halides, as well as rapid oxidation by O₂, to generate detectable Ni^III and/or Ni^IV intermediates and followed by C-C bond formation

Diastereoselective Attack on Chiral-at-Metal Ruthenium Allenylidene Complexes To Give Alkynyl Complexes

New chiral ruthenium­(II) allenylidene complexes were synthesized, and their reactivity with nucleophiles to give alkynyl complexes was investigated. The new allenylidene complex (<i>R</i>_Ru,<i>R</i>_ax)-[Ru­(Ind)­(PPh₃)­(<b>6</b>)­{CCC­(<i>t</i>-Bu)­(2-naphthyl)}]⁺PF₆^– was synthesized from the chloro precursor complex (<i>R</i>_Ru,<i>R</i>_ax)-[RuCl­(Ind)­(PPh₃)­(<b>6</b>)] and the racemic propargylic alcohol HCCC­(OH)­(<i>t</i>-Bu)­(2-naphthyl) and obtained in 96% yield, where (<i>R</i>_ax)-<b>6</b> is a chiral phosphoramidite and Ind an anionic indenyl ligand. The precursor and the allenylidene complex are chiral-at-metal, and the chiral information is completely transferred from the chloro precursor to the product allenylidene complex, both of which show the same absolute configuration, as demonstrated by X-ray diffraction. Together with the known allenylidene complex (<i>R</i>_Ru,<i>R</i>_ax)-[Ru­(Ind)­(PPh₃)­(<b>6</b>)­(CCCPh₂)]⁺PF₆^–, the attack of <i>n</i>-BuLi, MeLi, LiCCPh, and lithium 1-phenylethenolate nucleophiles on the allenylidene chain of (<i>R</i>_Ru,<i>R</i>_ax)-[Ru­(Ind)­(PPh₃)­(<b>6</b>)­{CCC­(<i>t</i>-Bu)­(2-naphthyl)}]⁺PF₆^– was investigated. The nucleophiles (Nu) reacted selectively with the gamma carbon of the allenylidene complexes to give the alkynyl complexes (<i>R</i>_Ru,<i>R</i>_ax)-[Ru­(Ind)­(PPh₃)­(<b>6</b>)­(CC–CPh₂Nu)] and (<i>R</i>_Ru,<i>R</i>_ax)-[Ru­(Ind)­(PPh₃)­(<b>6</b>)­{CC–C­(<i>t</i>-Bu)­(2-naphthyl)­Nu}] in 40% to 96% isolated yields. In the case of (<i>R</i>_Ru,<i>R</i>_ax)-[Ru­(Ind)­(PPh₃)­(<b>6</b>)­{CC–C*­(<i>t</i>-Bu)­(2-naphthyl)­Nu}], the gamma carbon C* becomes stereogenic upon attack of the nucleophiles. As assessed by ³¹P­{¹H} NMR, diastereodifferentiation took place, and the alkynyl complexes were isolated as diastereomeric mixtures with diastereomeric ratios between 60:40 and 84:16. The diastereodifferentiation originated only from the stereogenic metal center and the monodentate, chiral ligand. The study allows for investigation of stereoselective, nucleophilic attack of allenylidene complexes to give optically active, quaternary alkynes, which play a role in potential catalytic versions of nucleophilic substitution reactions of propargylic alcohols

Synthesis of a Smoothened Cholesterol: 18,19-Di-nor-cholesterol

Herein, we report the first synthesis of a demethylated form of cholesterol (18,19-di-nor-cholesterol), in which the C18 and C19 methyl groups of the β-face were eliminated. Recent molecular simulations modeling 18,19-di-nor-cholesterol have suggested that cholesterol’s opposing rough β-face and smooth α-face play necessary roles in cholesterol’s membrane condensing abilities and, additionally, that specific facial preferences are displayed as cholesterol interacts with different neighboring lipids and transmembrane proteins. Inspired by these poorly characterized biochemical interactions, an extensive 18-step synthesis was completed as part of a collaborative effort, wherein synthesizing a “smoothened” cholesterol analogue would provide a direct way to experimentally measure the significance of the β-face methyl groups. Starting from known perhydrochrysenone <b>A</b>, the synthesis of 18,19-di-nor-cholesterol was accomplished with an excellent overall yield of 3.5%. The use of the highly stereoselective Dieckmann condensation and the employment of Evans’ chiral auxiliary were both key to ensuring the success of this synthesis

The Aerobic Oxidation of a Pd(II) Dimethyl Complex Leads to Selective Ethane Elimination from a Pd(III) Intermediate

Oxidation of the Pd^II complex (N4)­Pd^IIMe₂ (N4 = <i>N</i>,<i>N</i>′-di-<i>tert</i>-butyl-2,11-diaza­[3.3]­(2,6)­pyridinophane) with O₂ or ROOH (R = H, <i>tert</i>-butyl, cumyl) produces the Pd^III species [(N4)­Pd^IIIMe₂]⁺, followed by selective formation of ethane and the monomethyl complex (N4)­Pd^IIMe­(OH). Cyclic voltammetry studies and use of 5,5-dimethyl-1-pyrroline-<i>N</i>-oxide (DMPO) as a spin trap suggest an inner-sphere mechanism for (N4)­Pd^IIMe₂ oxidation by O₂ to generate a Pd^III-superoxide intermediate. In addition, reaction of (N4)­Pd^IIMe₂ with cumene hydroperoxide involves a heterolytic O–O bond cleavage, implying a two-electron oxidation of the Pd^II precursor and formation of a transient Pd^IV intermediate. Mechanistic studies of the C–C bond formation steps and crossover experiments are consistent with a nonradical mechanism that involves methyl group transfer and transient formation of a Pd^IV species. Moreover, the (N4)­Pd^IIMe­(OH) complex formed upon ethane elimination reacts with weakly acidic C–H bonds of acetone and terminal alkynes, leading to formation of a new Pd^II–C bond. Overall, this study represents the first example of C–C bond formation upon aerobic oxidation of a Pd^II dimethyl complex, with implications in the development of Pd catalysts for aerobic oxidative coupling of C–H bonds

Aromatic Methoxylation and Hydroxylation by Organometallic High-Valent Nickel Complexes

Herein we report the synthesis and reactivity of several organometallic Ni^III complexes stabilized by a modified tetradentate pyridinophane ligand containing one phenyl group. A room temperature stable dicationic Ni^III–disolvento complex was also isolated, and the presence of two available <i>cis</i> coordination sites in this complex offers an opportunity to probe the C-heteroatom bond formation reactivity of high-valent Ni centers. Interestingly, the Ni^III-dihydroxide and Ni^III-dimethoxide species can be synthesized, and they undergo aryl methoxylation and hydroxylation that is favored by addition of oxidant, which also limits the β-hydride elimination side reaction. Overall, these results provide strong evidence for the involvement of high-valent organometallic Ni species, possibly both Ni^III and Ni^IV species, in oxidatively induced C-heteroatom bond formation reactions

Late First-Row Transition Metal Complexes of a Tetradentate Pyridinophane Ligand: Electronic Properties and Reactivity Implications

The synthesis and structural comparison are reported herein for a series of late first-row transition metal complexes using a macrocyclic pyridinophane ligand, <i>N</i>,<i>N</i>′-di-<i>tert</i>-butyl-2,11-diaza­[3.3]­(2,6)­pyridinophane (^tBuN4). The ^tBuN4 ligand enforces a distorted octahedral geometry in complexes [(^tBuN4)­M^II(MeCN)₂]­(OTf)₂ (M = Fe^II, Co^II, Ni^II, Cu^II), [(^tBuN4)­Zn^II(MeCN)­(OTf)]­(OTf), and [(^tBuN4)­Fe^III(OMe)₂]­(OTf), with elongated axial M–N_amine distances compared to the equatorial M–N_py distances. The geometry of [(^tBuN4)­Cu^I(MeCN)]­(OTf) is pentacoordinate with weak axial interactions with the amine N-donors of ^tBuN4. Complexes [(^tBuN4)­M­(MeCN)₂]­(OTf)₂ (M = Fe, Co) exhibit magnetic properties that are intermediate between those expected for high spin and low spin complexes. Electrochemical studies of (^tBuN4)­M complexes suggest that ^tBuN4 is suitable to stabilize Co^I, Ni^I, Co^III, Fe^III solvato-complexes, while the electrochemical oxidation of (^tBuN4)­NiCl₂ complex leads to formation of a Ni^III species, supporting the ability of the ^tBuN4 ligand to stabilize first row transition metal complexes in various oxidation states. Importantly, the [(^tBuN4)­M^II(MeCN)₂]²⁺ complexes exhibit two available <i>cis</i> coordination sites and thus can mediate reactions involving exogenous ligands. For example, the [(^tBuN4)­Cu^II(MeCN)₂]²⁺ species acts as an efficient Lewis acid and promotes an uncommon hydrolytic coupling of nitriles. In addition, initial UV–vis and electron paramagnetic resonance (EPR) studies show that the [(^tBuN4)­Fe^II(MeCN)₂]²⁺ complex reacts with oxidants such as H₂O₂ and peracetic acid to form high-valent Fe transient species. Overall, these results suggest that the (^tBuN4)­M^II systems should be able to promote redox transformations involving exogenous substrates